.... It is a rhythm and percussion instrument much used in Australian bush bands to provide timing for both the band with the melody and the dancers with their steps. Often the lagophonist is also the caller - the person who calls out to the dancers what the dance formations and steps will be.

After that I prefer to defer to  Martin Goreing in Darwin for his collection of definitions :

"Lagerphone or Murrimbidgee River Rattler. An upright pole with two crosspieces upon which are screwed beer bottle tops. The noise is made by hitting the instrument on the floor, at the same time striking the middle section with a with a solid piece of wood."  The Bushwhackers Australian Songbook

"Lagerphone - a home-made musical instrument made of beer-bottle tops, loosely nailed to a stick, which rattle when hit or tapped." - from   Strine decoded: An Australian / English on-line dictionary.

"A triumph of recycling technology and percussive versatility, this instrument is constructed from a number of lager bottle tops nailed to a broomstick handle, and when hit, makes a sound not unlike a number of lager bottle tops nailed to a broomhandle."

"Lagerphone - A 'bush' instrument made from bottle tops nailed onto a broomstick or other handy piece of wood. Paul bangs the lagerphone on the floor, scrapes it with a corrugated stick (called a 'whacker'), and jingles it about to add colour to the band's music. "   Bushwahzee homepage.

"And Jon, the bartender, had a tall wooden stick with a shorter crossmember near one end and several dozen beer bottle caps nailed close together over about half of its surface; this was referred to as a 'lagerphone'."